<p>表:&nbsp;<code>Employee</code></p>

<pre>
+-------------+------+
| Column Name | Type |
+-------------+------+
| id          | int  |
| salary      | int  |
+-------------+------+
Id是该表的主键列。
该表的每一行都包含有关员工工资的信息。
</pre>

<p>&nbsp;</p>

<p>编写一个SQL查询来报告 <code>Employee</code> 表中第 <code>n</code> 高的工资。如果没有第 <code>n</code> 个最高工资，查询应该报告为&nbsp;<code>null</code> 。</p>

<p>查询结果格式如下所示。</p>

<p>&nbsp;</p>

<p><strong>示例 1:</strong></p>

<pre>
<strong>输入:</strong> 
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
| 2  | 200    |
| 3  | 300    |
+----+--------+
n = 2
<strong>输出:</strong> 
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| 200                    |
+------------------------+
</pre>

<p><strong>示例 2:</strong></p>

<pre>
<strong>输入:</strong> 
Employee 表:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100    |
+----+--------+
n = 2
<strong>输出:</strong> 
+------------------------+
| getNthHighestSalary(2) |
+------------------------+
| null                   |
+------------------------+</pre>
